1. Field of Invention
This invention relates to methods and apparatus for symbol estimation and a receiver.
2. Description of Related Art
As digital wireless communication systems are deployed around the world, the importance of providing clear and cost-effective communication services increases. Various obstacles include mitigating the effects of inter symbol interference (ISI) and co-channel interference (CCI) which result when transmitted signals travel along several paths to one or more intended receivers. When the difference in path lengths are relatively small, the multiple signal images arrive at almost the same time. However, as the difference in path lengths increase, the multiple signal images can appear as echoes of the transmitted signal and give rise to ISI and CCI.
Currently, ISI and CCI multipath time dispersion is mitigated by using some form of equalization, such as linear equalization (LE), decision feedback equalization (DFE), maximum likelihood sequence estimation (MLSE), and the minimum mean square linear equalization (MMSE-LE) with MLSE equalization providing the best performance.
Digital equalizers work by taking periodic samples of the received multiple signal images and removing the destructive components which are disbursed over a period of time. However, as the length of time covered by an equalizer increases, the required complexity and processing power of the maximum likelihood equalizer becomes prohibitive. Therefore, the time period covered by an equalizer, or response time, is often truncated to be less than the impulse response time of the transmitted signal, which degrades the performance of the maximum likelihood equalizer. Accordingly, there is a need for systems and methods that better equalized signals with ISI using a truncated response time.